If you click on the link, you will see a little map of the United States, with a black line drawn around it. From 1 January 2015, this means that if you want to sail inside the line (i.e. stop at most US ports apart from southern Florida), you have to use low sulfur fuel, which costs a fortune. Maryland port officials are unofficially estimating a cost increase of around $150 per passenger.

Carnival UK has kept this very quiet. I would imagine the first place we will see an effect is in less liners, such as Cunard and the Queens, doing the London-New York run, and the utter demise of any special offers on those routes.

Let me know if you spot anything, and I will post anything else I learn.